The present invention relates to semiconductor structures and circuits, and particularly to semiconductor structures and circuits that require bidirectional protection against electrostatic discharges.
An electrostatic discharge (ESD) event can occur in a semiconductor chip when a charged conductor (including the human body) discharges a current through the semiconductor chip. An electrostatic charge may accumulate on a human body, for example, when one walks on a carpet. Contact of a body part, e.g., a finger, to a device containing a semiconductor chip causes the body to discharge, possibly causing damage to the semiconductor device. A similar discharge may occur from a charged conductive object, such as a metallic tool. Static charge may also accumulate on a semiconductor chip through handling or contact with packaging materials or work surfaces.
Such an ESD event can cause failure of components in a semiconductor chip through current overloading or reverse biasing. For example, radio frequency (RF) circuits including an antenna and a radio frequency switch that enables transmission or reception of an RF signal are vulnerable to electrostatic discharge of both polarities because the voltage on the antenna may be positive or negative at the time of the electrostatic discharge. Further, such an electrostatic discharge may occur while the antenna is electrically connected to an output node of a power amplifier to be employed as a transmission line or while the antenna is electrically connected to an input node of a low noise amplifier as a reception line. Typically, the switch connected to the antenna enables the selection of the operation of the antenna as a transmission line or a reception line. In either case, the voltage on the antenna may be either positive or negative depending on the phase of the RF signal on the antenna.
Thus, an antenna that is attached to a radio frequency circuit, which is typically a semiconductor structure including multiple semiconductor devices such as field effect transistors and/or bipolar transistors, require protection against electrostatic discharge events of both polarities, i.e., electrostatic discharge events caused by excessive electrons and electrostatic discharge events caused by excessive holes.